Our initial survey of post-translational modification has indicated widespread variation (nine of fourteen loci exhibit second-site patterns of variation). These results suggest that a great deal of such variation might be detected by techniques of sufficient resolution. In order to detect variants not resolved by either traditional or gel-sieving techniques, much of the current year was devoted to developing a higher resolution electrophoretic procedure. The approach was to perturb the tertiary structure of proteins in a controlled way, and watch for variation in the protein's response to the perturbation, using gel sieving to monitor protein shape. In parallel, efforts were made to standardize gel sieving procedures to promote between-laboratory comparability. To assess the potential functional importance of this class of variation, comparisons were made between variants of their enzyme activity levels, substrate affinities, and thermal stability.